Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $49.37   5.726%   $52.1969   $52.20   $52.20   $52.20  
  Purchase #2 $194.87   3.772%   $202.2205   $202.22   $202.20   $202.20  
  Purchase #3 $102.59   4.406%   $107.1101   $107.11   $107.10   $107.10  
  Purchase #4 $46.82   8.247%   $50.6812   $50.68   $50.70   $50.70  
  Purchase #5 $93.53   7.848%   $100.8702   $100.87   $100.85   $100.90  
  Purchase #6 $47.94   3.132%   $49.4415   $49.44   $49.45   $49.40  
  Purchase #7 $162.69   13.181%   $184.1342   $184.13   $184.15   $184.10  
  7 purchase totals = $697.81       $746.6546   $746.65   $746.65   $746.60